Catalytic epoxidation of alkenes by the manganese complex of a reduced porphyrinogen macrocycle

Article abstract of DOI:10.1002/adsc.201100433

The present paper details the first application of a fully reduced meso-octamethylporphyrinogen macrocycle as an effective ligand for simple operative manganese-catalyzed alkene epoxidation. The efficiency of the novel catalyst was determined in the prese

Full text of DOI:10.1002/adsc.201100433

FULL PAPERS
DOI: 10.1002/adsc.201100433
Catalytic Epoxidation of Alkenes by the Manganese Complex of
a Reduced Porphyrinogen Macrocycle
+
a
+a
a
b
Frederic Bruyneel, Christophe Letondor, Bjorn Bastꢀrk, Andrea Gualandi,
a
c
a,
Anca Pordea, Helen Stoeckli-Evans, and Reinhard Neier *
a
Institute of Chemistry, Neuchꢁtel University, Rue Emile-Argand 11, CP 158, CH-2009 Neuchꢁtel, Switzerland
Fax : (+41)-(0)32-718-2511; phone: (+41)-(0)32-718-2428; e-mail: reinhard.neier@unine.ch
Dipartimento di Chimica “G. Ciamician”, Universitꢂ di Bologna, via Selmi 2, I-40126 Bologna, Italy
Institute of Physics, Neuchꢁtel University, Rue Emile-Argand 11, CP 158, CH-2009 Neuchꢁtel, Switzerland
b
c
+
These two authors contributed equally to this work
Received: May 26, 2011; Revised: October 19, 2011; Published online: February 1, 2012
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/adsc.201100433.
Abstract: The present paper details the first applica- additives influenced the reactivity only moderately.
tion of a fully reduced meso-octamethylporphyrino- cis-Stilbene and 3b-acetoxy-5-cholestene were epoxi-
gen macrocycle as an effective ligand for simple op- dized in a stereoselective manner. The X-ray struc-
erative manganese-catalyzed alkene epoxidation. tures of the new manganese complexes were deter-
The efficiency of the novel catalyst was determined mined and showed a rigid planar coordination geom-
in the presence of various oxidants, apical ligands etry of the saturated macrocyclic ligand to the metal
and acidic/basic additives. Higher reactivity was centre.
found in favour of electron-rich alkenes, whereas an
electron-deficient conjugated alkene appeared as a
poor substrate in the screening. Sulfur additives were Keywords: epoxidation; manganese; nitrogen li-
active as apical ligands, whereas nitrogen-containing gands; tetraaza-macrocycles
Introduction
well-suited for the stabilization of high-valent metal-
oxo intermediates, which are believed to be the active
[5]
Oxidations of unfunctionalized hydrocarbons are of oxygen transfer species during these reactions. Non-
importance in organic chemistry and have been in- porphyrin iron and manganese complexes, as mimics
[6]
[
1]
tensely studied. Yet, a number of challenges remain of non-heme enzymes, were also intensively studied.
for the development of oxidation processes, such as They present the advantage of being more accessible
[6c]
the improvement of the chemo-, regio- and stereose- and readily tunable compared to porphyrins.
A
lectivity and the use of inexpensive and environmen- wide variety of ligands with N-donor and O-donor
[
2]
tally friendly catalytic metals and oxidants. Inspired functionalities, from bidentate to pentadentate and
by naturally occurring metalloenzymes, chemists have forming mono- or dinuclear metal centres have been
invested their efforts in designing biomimetic metal- designed for modelling the active site of non-heme
based catalysts, with the goals of understanding the enzymes and for developing catalytic alkane hydroxy-
mechanistic details of biochemical dioxygen activation lations, alkene epoxidations and alkene dihydroxyla-
and oxygen transfer reactions and of developing tions. Relevant structures include: triazacyclononane
[
3]
[7]
[8]
novel oxidation technologies. The first and some of derivatives, the salen family, saturated tetra- and
[
9]
the most studied catalysts in the field were the iron- pentaaza-macrocycles and the polypyridineamine li-
and manganese-porphyrin derivatives, which were in- gands related to the tris(pyridin-2-ylmethyl)amine
vestigated as chemical models of heme enzymes and (TPA) family. Their reactivity can be tuned by the
were shown to perform alkane and alkene oxidations coordination environment around the metal: the
in the presence of a variety of oxidants. The planar common tetradentate ligands, for example, form hexa-
and electron-rich structure of metalloporphyrins is coordinate mononuclear metal complexes with two
[
10]
[
4]
428
ꢃ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2012, 354, 428 – 440

Catalytic Epoxidation of Alkenes by the Manganese Complex of a Reduced Porphyrinogen Macrocycle
ligands occupy the trans, axial positions. An iron-
cyclam hydroperoxide complex was proposed to be
the reactive oxygen transfer species in alkene epoxi-
[
9a]
dations. Therefore, we envisaged the study of mac-
rocycle 1 as a ligand in metal-catalyzed oxidation,
speculating that the rigid and saturated ligand struc-
ture would provide stability of the metal complex,
while the presence of the unique array of hydrogen
bonds might influence the process of substrate recog-
nition.
Manganese tetradentate planar complexes such as
salens and porphyrins have been widely used for the
[
4a,8c,13]
epoxidation of olefins.
From an environmental
and economical point of view, the use of hydrogen
peroxide as terminal oxidant represents an alternative
to molecular oxygen, which is the cheapest and least
polluting oxidant, but offers a poor chemoselectivi-
[
13b,14]
ty.
The main challenges that have to be over-
come for the effective use of H O are: the suppres-
2
2
[
15]
Scheme 1. Synthesis of the Mn-calix[4]pyrrolidine complexes sion of the catalase activity, i.e., the catalytic dismu-
and 3.
2
tation of H O into H O and O , leading to fast oxi-
2
2
2
2
dant depletion; the formation of unselective HOC radi-
cals by the homolytic cleavage of the weak peroxo
additional labile ligands on the metal centre. Depend- OÀO bond; as well as the oxidative destruction of the
[
4a]
ing on whether these labile sites are located trans or catalysts by H O . The effective epoxidation of ole-
2
2
cis to each other, a different chemoselectivity can be fins by Mn catalysts and H O as terminal oxidant has
2
2
observed: for example, with non-heme iron catalysts, been achieved with halogenated porphyrin derivatives
cis-coordination sites are required for the cis-dihy- and with salen ligands, in the presence of carboxylic
droxylation reaction, while the epoxidation of olefins acid and nitrogen-containing additives, such as imida-
[
13,16]
can be catalyzed by complexes with trans or cis open zole, or by using anhydrous H O adducts.
coordination sites.
Dinu-
clear triazacyclononane and pyridylamine complexes
On the other hand, it has been demonstrated that were also shown to promote alkene epoxidation in
2
2
[
10b,c]
[
13]
planar and rigid macrocycles impart high kinetic and the presence of H O . Most of these oxygen trans-
2
2
[
11]
thermodynamic stability to their complexes. The re- fer processes have been proposed to proceed through
duced conformational mobility of the uncomplexed a high-valent oxo-manganese moiety, Mn(V)=O, sta-
ligand and its predisposition for complexation reduces bilized by electron density donation from ligands con-
the entropic penalty for complex formation and there- taining both s- and p-electron systems. On the contra-
by increases the stability of the metal complexes. ry, ligands containing only s-donors, such as tertiary
During our studies of the hydrogenation of calix[4]- amines, were shown to stabilize only intermediate oxi-
pyrroles we were able to isolate the fully reduced por- dation states of manganese, from Mn(II) to
[
9b]
phyrinogen macrocycle 1 (Scheme 1), able to function Mn(IV).
as a non-porphyrin ligand for metal binding.
An Mn(IV) complex of such a cross-
Al- bridged cyclam ligand was proposed to promote
though fully saturated, this novel tetraaza-macrocycle alkene epoxidation by Lewis acid activation of hydro-
[
12]
[
17]
shows a “disc-like”, almost planar conformation in gen peroxide. Oxygen transfer by Lewis acid activa-
the crystal. The four basic nitrogen atoms were shown tion of peracetic acid by iron and manganese metal
to function as efficient chelating ligands for transition complexes has also been suggested.
metals such as Cu, Ni, Pd, with the four pyrrolidine In this study, we report on the synthesis and the
[
18]
NÀH bonds pointing in a parallel direction orthogonal structure of a new manganese-calix[4]pyrrolidine che-
to the plane of the disk. The rigid planar coordination late, containing four tertiary nitrogen donors and no
geometry of the metal complexes of ligand 1 can be p-electron system, and on its catalytic activity in
compared to the metalloporphyrin scaffolds, whereas olefin epoxidation using H O as stoichiometric oxi-
2
2
the electronic effect of the saturated macrocyclic dant.
ligand on the manganese centre should be considera-
bly different. In the chemistry of saturated tetraaza-
macrocycles,
cyclam) also binds metal ions in a square planar fash-
ion, forming octahedral complexes in which the labile
1,4,8,11-tetraazacyclotetradecane
(
Adv. Synth. Catal. 2012, 354, 428 – 440
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Frederic Bruyneel et al.
FULL PAPERS
Results and Discussion
Synthesis and Characterization of the Manganese
Complexes 2 and 3
Complex 2 was readily prepared by mixing one equiv-
alent of the calix[4]pyrrolidine 1, obtained by reduc-
tion of calix[4]pyrrole, with one equivalent of
Mn ACHTUNGTRENNUNG( OAc) in deoxygenated ethanol at 808C for two
2
hours (Scheme 1). Removing the solvent afforded a
white-beige powder which was characterized by mass
spectroscopy as a mono-cationic complex bearing one
acetate ligand corresponding to the peak at m/z=
+
5
58.3 [M] . The preparation of suitable crystals of
complex 2 for X-ray diffraction analysis proved to be
challenging and could finally be achieved by slow dif-
fusion of diethyl ether into a solution of complex 2 in
tetrahydrofuran.
Washing the complex with brine afforded the corre-
sponding dichloro complex 3 which could be crystal-
lized easily. Complex 3 was characterized by mass
spectroscopy detecting the mono-cationic complex
bearing one chloride ligand with a molecular peak at
+
m/z=534.3 [M] and showing the typical isotope dis-
tributions for the metal and the chlorine. As expected,
complexes 2 and 3 were quite stable and could be
kept under nitrogen during months without noticeable
alteration of their properties.
The crystal structures of the acetate complex 2 and
[
19]
the chloro complex 3 are similar (Figure 1). More-
over, they are closely related to the structures of
[
12a]
other metal complexes reported earlier
and have a
similar conformation of the metal-free ligand in the Figure 1. (a) Molecular structure of complex 2 with thermal
[
12b]
ellipsoids drawn at the 50% probability level. Selected bond
crystal.
The rigid, planar structure of ligand 1 fa-
distances (ꢄ): MnÀO1 2.395(11); MnÀO3 2.081(13); MnÀN
vours the formation of tetradentate metal complexes
similar to the ones of aromatic porphyrins and phtha-
locyanines, with four occupied “equatorial” coordina-
tion sites and leaving open the two “axial” positions
at the metal centre. These structures are considerably
different from the ones formed by many aliphatic pol-
yaza-macrocycles, which usually prefer the formation
of complexes bearing two open cis-coordination sites.
The manganese cation and the nitrogen atoms of
2
.198(14)–2.221(13). (b) Molecular structure of complex 3
with thermal ellipsoids drawn at 50% probability level. Se-
lected bond distances (ꢄ): MnÀCl1 2.406(7); MnÀCl2
2
.909(6); MnÀN 2.205(16)–2.221(16); NÀH···Cl2 2.77–2.83.
[
Mn violet; N blue; O red; Cl green; H grey sticks; C-bound
H-atoms have been omitted for clarity].
the four pyrrolidine rings form a plane. The bond metal complexes of the calix[4]pyrrolidine ligand
[
12a]
length between the nitrogen of the pyrrolidine and 1.
The two faces of the manganese complexes are
the manganese (2.198–2.221 ꢄ for complex 2 and clearly differentiated. Four of the meso-methyl groups
2
.205–2.221 ꢄ for complex 3) are slightly longer than are in the plane extending away from the metal
[15]
those typically found in metalloporphyrins (2.01 ꢄ).
centre (“equatorial” positions), while the other four
The two anions (acetate or, respectively, chloride meso-methyl groups are in an orthogonal position to
ions) occupy the two apical positions on a distorted the plane, pointing in the same direction as the pyrro-
octahedron (Figure 1). One of the anion ligands is di- lidine NÀH bonds (“axial” positions) and forming a
rectly bound to the manganese (2.081 ꢄ for complex shallow hydrophobic cavity. This is in contrast to the
2
and 2.406 ꢄ for complex 3) and the other anion is porphyrin- and phthalocyanin-metal complexes,
held in place (2.395 ꢄ for complex 2 and 2.909 ꢄ for where the two sides of the planar metal complexes
complex 3) by a hydrogen bond network provided by are identical. As a consequence, separate modifica-
the four NH on the four pyrrolidine rings. This pecu- tions of the two faces of the Mn complexes 2 and 3
liar arrangement has already been observed for other and the study of such modifications on the conforma-
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Adv. Synth. Catal. 2012, 354, 428 – 440

Catalytic Epoxidation of Alkenes by the Manganese Complex of a Reduced Porphyrinogen Macrocycle
tional behaviour and on the properties of the com- 0.7 mol% of complex 2 and 6 equivalents of H O ,
2
2
plexes can be envisaged.
added in two portions (Table 1, entries 1–4). Benzal-
dehyde was obtained as the only side-product of the
reactions, in less than 6% yield in all cases. The reac-
tion in acetonitrile was faster than in acetone. The
Epoxidation of Olefins Catalyzed by the Manganese
Complex 2
[
22]
Radziszewski reaction,
leading to the epoxidation
via peroxyacetimidic acid and without the interven-
[
23]
Preliminary experiments using hydrogen peroxide in tion of the catalyst 3 could be ruled out. 2-Propanol
acetone, complex 3 as catalyst and styrene as sub- also gave satisfactory yields (Table 1, entry 5), where-
strate led only to low conversions into styrene oxide, as the biphasic system with CH Cl was inefficient in
2
2
while an efficient catalase activity could be ob- our case, as only 6% of the corresponding epoxide
[20]
served.
It is known from the literature that the was obtained after 90 min (Table 1, entry 6). This was
presence and the electronic properties of the axial probably due to a poor contact between the oxidant
ligand strongly influence the oxygenase and catalase and the complex in the biphasic system. Surprisingly,
[
21]
activities of metalloporphyrin complexes.
In our DMF was an unsuitable solvent for the reaction: nei-
case, replacing the chlorides of complex 3 by acetates ther the formation of epoxide nor of other oxidized
in complex 2 led to an increase in the yield of styrene products was observed (Table 1, entry 7).
oxide. We therefore concentrated our efforts on
As the next step we tested the effect of different
studying the catalytic activity of complex 2 and its ef- oxidants on the epoxidation of styrene in acetonitrile.
ficiency to catalyze the epoxidation of olefins. Styrene We compared H O , tert-butyl hydroperoxide
2
2
was chosen as a model substrate and the stoichiomet- (TBHP), (diacetoxyiodo)benzene [PhI
ACHTUNGTNERNGNU( OAc) ], iodo-
2
ric oxidant was a solution of H O in an acetone/ sylbenzene (PhIO) and sodium hypochlorite (NaOCl)
2
2
water mixture. Screening of several additional co-sol- as terminal oxidants. PhI ACHTUNGETRNN(UNG OAc) , PhIO and NaOCl
2
vents, either in a homogeneous phase or as a two- were ineffective and no styrene conversion was de-
phase system with the oxidant, indicated acetonitrile tected after 90 min and 1.8 equivalents of oxidant vs.
and acetone as the solvents that gave the best results, substrate (Table 1, entries 8–10). tert-Butyl hydroper-
leading to high epoxide yields after 90 min using oxide (3.6 equiv.) afforded 45% conversion, although
a significant amount of over-oxidized products was
formed (24%), identified by GC-MS as the corre-
Table 1. Influence of solvents and oxidants on the catalytic sponding aldehyde and diol, besides 21% of styrene
[a]
epoxidation of styrene.
epoxide (Table 1, entry 11). Hydrogen peroxide
3.6 equiv.) was by far the most active and selective
(
oxidant tested, as it afforded the highest conversion
into styrene epoxide and the lowest amount of over-
oxidized side-products (Table 1, entry 12).
Entry Co-solvent
Oxidant
Time
min]
Yield
[b]
The effect of several additives on the catalysis was
assessed subsequently. Additives can act as bases or
as axial ligands on the metal centre and thus may
change the structure and the reactivity of the catalyti-
[
[%]
1
2
3
4
5
MeCN/Me CO H O
30
90
30
90
90
82
95
50
95
80
2
2
2
2
2
2
2
MeCN/Me CO H O
2
2
[
4a,8c,13,24]
Me CO
H O
cally active species.
In particular, it was shown
2
2
Me CO
H O
that N-donor ligands such as imidazole derivatives
play a key role in Mn-porphyrin- or Mn-salen-cata-
lyzed olefin epoxidations by H O . We tested the in-
2
2
i-PrOH/
H O
2
Me CO
2
2
2
6
7
8
9
1
1
1
CH Cl /Me CO H O
90
90
6
0
0
1
0
21
67
2
2
2
2
2
fluence of a variety of additives on the styrene epoxi-
DMF/Me CO H O
2
2
2
dation catalyzed by complex 2 with H O in acetoni-
2
2
MeCN
MeCN
MeCN
MeCN
MeCN
PhI
A
H
U
G
R
N
U
G
2
[
c]
trile, by comparing the conversion into styrene oxide
obtained after 90 min in the presence and in the ab-
sence of the additive. It is noteworthy that the com-
monly used nitrogenous base additives, which strongly
modulate the reactivity of salen, porphyrin and
cyclam metal-complexes, proved to be either detri-
mental or ineffective in our case. Addition of sodium
acetate, sodium chloride, imidazole, or pyridine to the
reaction mixture did not lead to a significant change
in the result. On the contrary, the addition of phenol
or N-methylmorpholine led to a 15% decrease, while
PhIO
NaOCl
TBHP
H O
90
90
90
90
0
1
2
2
2
[
a]
Reactions were carried out at 0–38C with 0.7 mol% com-
plex 2. The oxidant was added in two equal portions, at
the beginning of the reaction and after 60 min (total
6
equiv. vs. styrene for entries 1–7; 1.8 equiv. for en-
tries 8–10 and 3.6 equiv. for entries 11 and 12).
The relative amount of epoxide formed was determined
by GC.
[
[
b]
c]
PhIO was mostly insoluble in the reaction mixture.
Adv. Synth. Catal. 2012, 354, 428 – 440
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431

Frederic Bruyneel et al.
FULL PAPERS
sulfur additive on the catalysis, several oxidized sulfur
compounds were selected and used under the opti-
mized conditions as additives in the catalytic epoxida-
tion of styrene by H O (4 mol% sulfur-containing ad-
2
2
ditive, 90 min reaction time, 3.7 equiv. H O ). A
2
2
slightly lower substrate concentration compared to
the previous experiments ([substrate]=2 mM) can ac-
count for a small loss in the yield of styrene oxide in
the reference reaction without additive (60% vs. 67%
reported Table 1, entry 11). With the exception of thi-
oanisole (PhSMe), for which a slight decrease in the
epoxide yield was observed, almost all the additives
led to an increase of the reactivity (Figure 3). The
best results were obtained with thiophenol and
phenyl disulfide, which led to a relative increase in
yield of 37–39% compared to the same reaction with-
Figure 2. Conversion of styrene into styrene oxide as func-
tion of the molar ratio of thiophenol vs. substrate. The reac- out additive.
tion was performed in acetonitrile with a ratio catalyst/sub-
Dimethyl sulfoxide slightly improved the epoxide
strate/H O 1/140/504 and [substrate]=2.4 mM.
2
2
yield (10%), but unfortunately these experiments
were not reproducible for unexplained reasons.
Phenyl sulfinate and phenyl sulfonate had a smaller
DMAP lowered by 60% the yield of styrene oxide influence of the catalysis and only moderately im-
compared to the same reaction without additive. proved the yield, by 26% and 16%, respectively. At
Considering the importance attributed to the thio- this stage, the exact nature of the axial ligand (thio-
[
5d,25]
late ligands in natural systems,
we tested thiophe- late or oxidized species thereof) remains unknown.
We then proceeded to test the efficacy of the epoxi-
nol as additive. Its addition led to a significant en-
hancement of the reactivity, with a 30% increase in dation process in the presence of several acidic and
styrene oxide yield, compared to the reaction without basic additives. When a large excess (310 equiv. vs.
additive. In order to determine the best ratio of thio- catalyst) of the strong methanesulfonic acid was
phenol vs. substrate, a series of reactions was conduct- added, no epoxidation was observed. Interestingly, a
ed varying the molar ratio of thiophenol (Figure 2). large excess of acetic acid (350 equiv. vs. catalyst) in-
Maximum conversion into styrene oxide was reached creased the yield of styrene oxide to almost 80%. The
when 4 mol% of thiophenol (vs. styrene) were added presence of either acetic acid or methanesulfonic acid
to the reaction mixture, and dramatically decreased (MSA) in smaller quantities (4-fold excess compared
with higher amounts of additive.
to the catalyst) modulated the reactivity of the cata-
Thiolate ligands were shown to influence the reac-
tivity of the iron centre in non-heme iron complexes,
[
5c,25b,26]
by increasing the electron density on the metal.
This decreases its oxidation potential and thereby the
energy required for the cleavage of the OÀO bond
and formation of the oxo-species. In addition, the
electron-rich thiolate competes with the oxo-group
for the d orbitals, thus weakening the Fe=O bond.
p
Although the energy match between the d orbitals of
the metal and the orbitals on sulfur is usually poorer
for the manganese divalent cations than for the iron
[27]
cations, a similar effect of the thiolate on a MnÀO
bond could explain the beneficial effect of thiophenol
on the styrene epoxidation catalyzed by complex 2.
An obvious drawback of the use of thiophenol as
an additive is its susceptibility to oxidation in the
Figure 3. Effect of additives containing a sulfur atom in dif-
ferent oxidation states on the catalytic epoxidation of sty-
[
28]
rene by complex 2 and H O . The reaction was performed
2 2
presence of peracids and peroxides. Sulfoxides, sul-
fonates and disulfides are known to be good ligands
in acetonitrile with a ratio catalyst/additive/substrate/H O2
2
1
/5.6/140/520 and [substrate]=2 mM. The variation in yield
[
29]
in several transition metal complexes and they have
already been used to both modulate the catalytic ac-
tivity and anchor the catalyst on a solid surface.
was calculated relative to the process without the additive,
which gave 60% yield. The experiments were made in tripli-
To cate, standard deviation from the mean was 10% for DMSO
[
29c]
investigate the effect of the level of oxidation of the and <3% for the others.
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Adv. Synth. Catal. 2012, 354, 428 – 440

Catalytic Epoxidation of Alkenes by the Manganese Complex of a Reduced Porphyrinogen Macrocycle
[
32]
peroxides in the presence of H O . Lewis acid acti-
2
2
vation of a peroxymonocarbonate by manganese or
2
Mn-oxo formation from a h -peroxycarbonate com-
plex have been envisaged as plausible mechanisms for
[
32a]
the oxygen transfer.
The “disc”-like arrangement
of complex 2 and the unavailability of two open cis-
coordination sites, necessary for the formation of the
2
h -peroxycarbonate complex, suggest a possible Lewis
acid-type of activation in our case.
Having established the reactivity profile of our cat-
alyst in the presence of several oxidants, axial ligands
and basic/acidic additives with a model substrate, we
proceeded to investigate the substrate scope of the
Figure 4. Effect of acidic and basic additives on the catalytic
epoxidation of styrene by complex 2 and H O . The reaction
was performed in acetonitrile with a ratio catalyst/additive/
2
2
novel catalyst under optimized conditions, using H O2
2
in acetonitrile and thiophenol as additive. The results
of this screening are summarized in Table 2. Under
these conditions, reasonable to high conversions into
substrate/H O 1/4/140/520 and [substrate]=2 mM. The var-
2
2
iation in yield was calculated relative to the process without
the additive, which gave 60% yield.
[a]
Table 2. Epoxidation of representative alkenes.
lyst (Figure 4). Only 33% of the styrene was convert-
ed when MSA was added (corresponding to a de-
crease in reactivity of 27%), probably due to a de-
composition of the catalyst into protonated ligand
and free Mn(II), which is an ineffective epoxidation
catalyst under these conditions. Moreover, a signifi-
cant amount of diol (23%) was formed, probably be-
cause of acid-catalyzed ring opening of the epoxide
by water, while only 10% of styrene epoxide could be
detected. On the contrary, the addition of acetic acid
led to clean epoxidation and increased the styrene
oxide yield by 27% (from 60% to 87%). It has al-
ready been reported that acetic acid can increase the
efficiency of epoxidation catalysts with H O and
Entry Alkene
1
Epoxide yield
after 40 min [%] after 90 min [%]
Epoxide yield
45
65
82
[b]
[b]
2
3
4
5
0
[
c]
[c]
37/6
46/11
2
2
most of the reported complexes adopt a conformation
with two open cis-coordination sites. Que and co-
workers found that polypyridyl-polyamine Fe com-
plexes catalyze the in situ formation of peracetic acid
[
d]
[d]
0
0
8
[
d]
[d]
[e]
5
(60)
(
AcOOH) from H O and AcOH, which in turn en-
2 2
[
18c]
hances the epoxidation efficiency.
Peracetic acid
6
88
96
was reported as an efficient oxidant with Fe- and Mn-
[18]
based catalysts.
On the other hand, Jacobsen and
7
8
9
57
6
85
11
0
co-workers proposed an Fe-dipyridyl-diamine-based
system in which the role of AcOH was to generate an
[
10d]
acetate-bridged diiron
A
H
U
G
E
N
N
(III) complex.
Manganese-
catalyzed oxidations with H O and acetic acid as ad-
0
2
2
ditive have received attention over the last years, al-
though the exact nature of the oxidizing species is not
[
a]
Reactions were carried out in acetonitrile at 0–38C with
a molar ratio catalyst/thiophenol/substrate/H =1/5.6/
40/520 and [substrate]=2 mM. The oxidant was added
[30]
known. Moreover, other carboxylic acids and car-
boxylate salts have also been shown to increase the
O
2 2
1
[
30b,31]
in 3 portions, at t=0, 30 and 60 min. The epoxide yield
was determined by GC using benzonitrile as internal
standard (see Experimental Section).
b]
hydrocarbon oxidation activity of Mn complexes.
The presence of dihydrogen phosphate was detri-
mental for the catalysis (Figure 4). On the contrary,
addition of a bicarbonate solution led to an improve-
ment of the styrene oxide yield by almost 20%. Bur-
gess et al. have reported the efficient epoxidation of
alkenes by manganese salts in the presence of bicar-
bonate and it is known that bicarbonates can form
[
Extensive proportion of side-products appeared during
the reaction.
Yield of cis-/trans-stilbene oxide.
[c]
[d]
6
0% DMF was used as co-solvent to improve substrate
solubility.
[e]
Yield of indene oxide obtained using 15% DMF.
Adv. Synth. Catal. 2012, 354, 428 – 440
ꢃ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
433

Frederic Bruyneel et al.
FULL PAPERS
epoxide were obtained for aromatic and for cyclic al-
Different mechanisms have been proposed in the
kenes (Table 2, entries 1–7), whereas the linear ali- literature for the manganese-catalyzed alkene epoxi-
phatic 1-octene reacted more slowly (Table 2, dation, depending on the specific catalysts and reac-
entry 8). The best yield (96% of epoxide) was ach- tion conditions (Scheme 2). For mononuclear com-
ieved for norbornene (Table 2, entry 6). The electron- plexes of porphyrins and salens, the most well-known
poor cyclohexenone was completely unreactive and is the oxygen rebound mechanism, in which the man-
afforded no oxidized product, even after a longer re- ganese catalyst reacts with the oxidant to form
action time (Table 2, entry 9). The electron-rich p-me- Mn(V)=O, which then transfers the oxygen atom to
thoxystyrene reacted faster, but in a less selective the substrate in a concerted or in a stepwise manner
[
8c,33]
manner (Table 2, entry 2), affording considerable (pathway a in Scheme 2).
amounts of over-oxidized by-products and epoxide lective Mn(IV)=O species has also been proposed as
A less reactive and se-
[
34]
ring opening.
a possible intermediate. With H O or alkyl hydro-
2 2
As expected, the disubstituted non-cyclic alkenes peroxides as oxidants, a radical mechanism might
cis- and trans-stilbene reacted slower than styrene and occur, leading to non-selective epoxidation (pathway
[
4a]
the cis-substituted derivative was more reactive than b in Scheme 2). Finally, the Lewis acid activation of
its trans counterpart (Table 2, entries 3 and 4). Only the oxidant by the Mn complex without redox partici-
8
% of trans-stilbene oxide was obtained, probably pation of the manganese atom, such as in adducts like
[35] + [17b]
due to the poor solubility of the substrate. Even when Mn
A
H
U
G
R
N
U
G
or Mn(IV)(=O)
A
H
U
G
E
N
N
(OOH) ,
has also
60% DMF were used in the solvent mixture, trans- been proposed (pathway c in Scheme 2).
stilbene was not completely soluble at the early stage
The stereoselectivity of cis-alkene epoxidation has
of the reaction. Moreover, DMF has been shown to been intensely studied, as it can give important infor-
be a poor solvent for the catalytic epoxidation (see mation on the epoxidation mechanism. A stereoselec-
above), which could account for the low substrate tive cis-epoxidation is favoured by a concerted mech-
conversion under these conditions. The same solubili- anism [from the Mn(V)=O species or by Lewis acid
ty problem was encountered in the case of indene, an activation of the oxidant), while cis/trans isomerisa-
aromatic cyclic alkene that was expected to show rea- tion is an indication of a stepwise, radical mechanism.
sonable reactivity. The use of 60% DMF in the reac- The epoxidation of cis-stilbene by complex 2 occurs
tion mixture was necessary for substrate solubiliza- with moderate yield and mostly retention of the rela-
tion, but had a negative effect on the result. In this tive configuration (Table 2, entry 3), although a signif-
case, however, decreasing the amount of DMF from icant quantity of trans-stilbene oxide was produced
6
0% to 15% in acetonitrile significantly improved the along with the desired cis-stilbene oxide product (cis:-
yield of the corresponding epoxide, from 5% to 60% trans ratio 17:83). Given the saturated nature of the
Table 2, entry 5). chelate ligand 1, stabilization of an Mn(V)=O inter-
(
[
9b]
mediate appears unlikely.
Oxidation to the
Scheme 2. Different mechanisms accounting for the stereoselective or non-stereoselective epoxidation of cis-alkenes with
manganese complexes.
434
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Adv. Synth. Catal. 2012, 354, 428 – 440

Catalytic Epoxidation of Alkenes by the Manganese Complex of a Reduced Porphyrinogen Macrocycle
Figure 5. GC traces of the reaction mixture with complex 2 showing residual cholesteryl acetate and the corresponding b-
and a-epoxides. In the insert the b- and a-epoxides produced in the control reaction with m-CPBA.
+
5
Mn(IV)(=O)(OH) species and Lewis acid activation Mn-catalyzed b-epoxidation of D -steroids include
[
38]
of hydrogen peroxide, as proposed by Busch et al. Mn-porphyrins
with their cross-bridged cyclam derivatives, is more KMnO +t-BuOH in CH Cl ). Complex 2 was used
and the Parish reagent (CuSO /
4
[39]
4
2
2
plausible to be the main mechanism in our case, al- under slightly modified experimental conditions com-
though a non-stereoselective mechanism giving the pared to the optimized styrene epoxidation, in that
trans-epoxide also occurs. This hypothesis is support- addition of ethyl acetate (20% in acetonitrile) was re-
ed also by the fact that oxidants other than peroxides quired to ensure the complete solubility of the sub-
[40]
[
NaOCl, PhI
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(OAc) , PhIO] are completely unreactive strate and a higher amount of oxidant was used.
A
2
with our complex. Moreover, this type of electrophilic control reaction using mCPBA as the organic peracid
delivery of the oxygen atoms to the substrates would was performed as reported in the literature and the
favour higher yields with electron-rich alkenes, which corresponding a- and b-epoxides were used as refer-
was observed with p-methoxystyrene. Lewis acid acti- ences for GC analysis. A representative epoxidation
vation of a peroxymonocarbonate or of a peracetic result is shown in the Figure 5.
acid species could be also easily explained with this
mechanism.
Clean conversion of the substrate into the corre-
sponding epoxides was observed with complex 2 and
To further test the selectivity of our oxidation H O , with 15% and 40% yield in the absence and in
2
2
system, we investigated the epoxidation of the unsatu- the presence of thiophenol, respectively. The diaste-
5
rated D -steroid 3b-acetoxy-5-cholestene. Direct epox- reoselectivity of the epoxidation catalyzed by complex
idation of this type of compound with organic peroxy 2 was inversed compared with the selectivity observed
acids, such as mCPBA, affords mainly a-epoxides and for the peracid epoxidation. The observed b:a-epox-
this diastereoselectivity is attributed to the steric hin- ide ratio was 70:30, whereas a ratio of 28:72 was ob-
drance between the organic peracid and the C-10 an- tained with mCPBA. To the best of our knowledge,
[
36]
gular methyl group during the epoxidation. In con- this is the first non-porphyrin manganese complex re-
4
5
5
trast, the catalyzed epoxidation of D - and D -unsatu- ported for the b-selective oxidation of D -steroid de-
rated steroids is usually b-selective.
[
36b,37]
Examples of rivatives.
Adv. Synth. Catal. 2012, 354, 428 – 440
ꢃ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
435

Frederic Bruyneel et al.
FULL PAPERS
Conclusions
À1
ter. Peaks are reported in cm with the following intensi-
ties: s (strong, 67–100%), m (medium, 34–66%), w (weak,
1
–33%). Low-resolution electrospray (ESI) mass spectra
In summary, we have synthesized a novel manganese
non-porphyrin catalyst, using the conformationally
rigid and saturated calix[4]pyrrolidine 1 as ligand. The
Mn(II) cationic complex, bearing acetate ions as axial
ligand and as counterion, displayed interesting cata-
lytic properties. Epoxidation of simple alkenes using
were recorded on a Finnigan LCQ mass spectrometer at the
University of Neuchꢁtel. Analytical GC-MS were performed
using the gas chromatograph Polaris Q-Trace GC (Finnigan)
fitted with a flame ionization detector (H carrier gas,
1
2
À1
mLmin , detector temperature 3008C) and a ZB-5MS
column (30 mꢅ0.25 mmꢅ0.25 mm) and mass spectra were
hydrogen peroxide as terminal oxidant gave reasona- acquired in EI mode (70 eV). GC retention times (t ) and
r
ble to good yields of product. Our catalyst displays integrated ratios were obtained from reporting integrators
good robustness in acidic media. The addition of po- without corrections for different sensitivities. Analyical GC
experiments were recorded on an Agilent 6850 equipped
tential apical ligands led to an unusual reactivity pat-
with a column Agilent HP-1 (30 m ꢅ 0.32 mmꢅ0.25 mm)
tern. Most of the ligands known to accelerate epoxi-
dation were not effective, whereas the sulfur contain-
ing ligands showed interesting effects. Addition of thi-
ophenol afforded the most significant increase in the
reactivity of our catalytic system, with formation of
the epoxide products in high yields. The saturated tet-
fitted with a flame ionization detector (H carrier gas,
2
À1
1
mLmin ). The detector temperature was set at 3008C.
GC retention times (t ) and integrated ratios were obtained
r
from reporting integrators without corrections for different
sensitivities. Benzonitrile or eicosane was used as internal
standard and the calibration of the detection was carried out
raaza ligand and the absence of a p-electron donor for each alkene and corresponding epoxide relative to the
system to stabilize the high-valent Mn(V)=O led to internal standard. All the reagents (including substrates, ep-
the hypothesis of a Mn(IV) hydroperoxide adduct as oxides for GC references and additives) were purchased
from Aldrich or Acros and used as such unless their synthe-
ses according to literature is specified.
the active intermediate in epoxidation, by analogy
with the cross-bridged saturated Mn-cyclam com-
plexes already reported in the literature. A mechanis-
General Procedure for the Preparation of Mn
Complexes 2 and 3
tic study of the system is currently underway. Prelimi-
nary results are in accordance with the proposed type
of Lewis acid activaton: the epoxidation of cis-stil-
[12]
Calix[4]pyrrolidine 1
(80 mg, 0.18 mmol, 1 equiv.) and
bene provides cis-stilbene oxide as the dominant Mn
ACHTUNGTRNEU(GN OAc) ·4H O (44 mg, 0.18 mmol, 1 equiv.) were placed
2 2
product and higher yields of epoxidation are obtained in a Schlenk tube under nitrogen, then EtOH (6 mL), previ-
with the electron-rich alkenes, suggesting an electro- ously deoxygenated by bubbling nitrogen for 30 min, was
added and the mixture stirred. The colourless solution was
philic delivery of the oxygen to the substrates. More-
heated at reflux for 2 h and the solvent removed under
over, this novel Mn-catalyst is the first non-porphyrin
5
vacuum to afford complex 2 as a white beige powder. The
acetate ligands of complex 2 were readily exchanged with
chloride ions, by washing four times a solution of complex 2
in CH Cl with a brine solution adjusted at pH 9 with
Mn complex to epoxidize the unsaturated D -steroid
b-acetoxy-5-cholestene with a reasonable yield and
3
b-selectivity.
2
2
K CO . The organic phases were dried with Na SO and the
2
3
2
4
solvent removed under vacuum to afford complex 3 as a
white powder (yield: 80%, 71 mg). Crystals of the two com-
plexes were obtained by slow diffusion of diethyl ether into
a solution of the corresponding complex in THF (white-
beige crystals for complex 2, white crystals for complex 3).
Experimental Section
General
All reactions were performed in oven-dried (1408C) or
flame-dried glassware under an inert atmosphere of dry N2
À1
Complex 2: C H MnN O , M.W. 617.38 gmol . IR
3
2
58
4
4
(KBr): n=3411 br, 3234 m, 2971 s, 2882 s, 1586 s, 1471 m,
using Schlenk techniques. Solvents for reactions were dis-
tilled from the indicated drying agents: diethyl ether (Na,
benzophenone), THF (Na, benzophenone), CH Cl (P O ),
1
383 s, 1265 vw, 1151 vw, 1056 s, 1003 s, 982 m, 912 m, 830
À1
vw, 654 w cm ; HR-MS (ESI positive mode): m/z=558.37,
calcd. for C H MnN O : 558.371; ESI-MS: m/z (%)=558.3
[MÀAcO ] (100), 559.4 (35), 560.4 (6).
2
2
2
5
3
0
55
4
2
acetonitrile (CaH ), dioxane (Na, benzophenone), DMF
À
2
(
CaH ), triethylamine (CaH ). Brine refers to a saturated
À1
2
2
Complex 3: C H Cl MnN , M.W. 569.29 gmol . IR
2
8
52
2
4
aqueous NaCl solution. Analytical TLC was performed on
silica gel plates with QF-254 indicator and visualization was
carried out under UV light (254 nm) and/or after treatment
with phosphomolybdic acid. Column chromatography was
performed with 230–400 mesh silica gel. Solvents for extrac-
tion and chromatography were of analytical grade. The
(
1
KBr): n=3443 brw, 3235 s, 2972 s, 2881 s, 1619 s, 1472 m,
453 s, 1418 s, 1403 m, 1373 m, 1267 m, 1151 m, 1058 s, 1028
À1
m, 1000 s, 982 s, 914 m, 830 vw, 631 vw, 561 vw, 541 vw cm ;
HR-MS (ESI positive mode): m/z=534.326, calcd. for
À
C H ClMnN : 534.32; ESI-MS: m/z (%)=534.3 [MÀCl ]
2
8
52
4
(
100), 535.3 (22), 536.3 (26), 537.3 (7).
1
13
H NMR and C NMR spectra were recorded on a DPX
00 Bruker Advance Fourier transform spectrometer in deu-
4
Crystal Structure Analysis of 2 and 3:
teriochloroform (CDCl ) with tetramethylsilane (TMS) as
3
internal standard at ambient temperature. Infrared spectra
Single crystals were obtained as colourless plates by diffu-
sion of diethyl ether into a solution of the complexes in tet-
(
IR) were recorded on a Fourier transform spetrophotome-
436
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ꢃ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2012, 354, 428 – 440

Catalytic Epoxidation of Alkenes by the Manganese Complex of a Reduced Porphyrinogen Macrocycle
1
rahydrofuran. The intensity data were collected at 173 K on
a Stoe Mark II-Image Plate Diffraction System equipped
with a two-circle goniometer and using MoKa graphite
monochromated radiation. The structures were solved by
3b-Acetoxy-5,6-a-epoxycholestane: H NMR (400 MHz,
CDCl ): d=4.89–5.00 (m, 1H, H-3), 2.90 (d, J =4.4 Hz,
3
H,H
1H, H-6), 2.02 (s, 3H, 3-OAc), 1.07 (s, 3H, H-19), 0.89 (d,
JH,H =6.6 Hz, 3H, H-21), 0.87 and 0.86 (2 d, J =6.5 Hz,
2ꢅ3H, H-26 and H-27), 0.64 (s, 3H, H-18), 2.20–0.90 (m,
28H); ESI-MS (a+b mixture): m/z (%)=467.6 (100) [M+
3
H,H
[41]
direct methods (SHELXS-97 ). The refinement and all fur-
[41]
ther calculations were carried out using SHELXL-97. The
H-atoms were included in calculated positions and treated
as riding atoms using SHELXL default parameters. Com-
pound 2 crystallized as a dihydrate but the water molecule
H-atoms could not be located. The non-H atoms were re-
fined anisotropically, using weighted full-matrix least-
+
Na] , 468.6 (35), 469.6 (20).
Indene oxide: This compound was prepared from the bro-
mohydrin derivative according to the procedure described in
the literature. The title product was isolated by bulb to
bulb distillation to afford the desired epoxide; isolated
[42]
2
1
3
squares on F . The non-H atoms were refined anisotropical-
yield: 68%. H NMR (400 MHz, CDCl ): d=7.5 (d, J
=
3
H,H
2
3
ly, using weighted full-matrix least-squares on F . For the
7.3 Hz, 1H), 7.3–7.18 (m, 3H), 4.28 (d, J =2.8 Hz, 1H),
H,H
3 2
crystal structure of 2, the O, N, and C atoms were refined
with the ISOR instruction, giving 250 least-squares con-
straints. The crystal of 3 was refined as a pseudo-merhedral
twin with a 2-fold rotation about the c-axis The final refined
BASF value is 0.3126(87). Structure 3 contains a solvent ac-
4.14 (dd, J =2.9 and 2.8 Hz, 1H), 3.23 (d, J =18 Hz,
H,H H,H
2 3 13
1H), 2.99 (dd, JH,H =18, JH,H =2.8 Hz, 1H); C NMR
(100 MHz, CDCl ): d=143.5, 140.8, 128.5, 126.2, 126.0,
125.1, 59.0, 57.6, 34.5; EI-MS: m/z (%)=104.12 (100)
[MÀCO] , 131.96 (48) [M] ; R (petrol ether/AcOEt 5:1)=
3
+
+
f
3
cessible void of 51 ꢄ , which equates to ca. one water mole-
0.5.
cule per unit cell. This was not taken into consideration for
the refinement of the structure. The crystals of both 2 and 3
diffracted very weakly beyond ca. 308 in 2q, despite expo-
sures times of 9 min per image. Hence, the high Rint and
final R values are in part due to the very poor quality of the
crystals and the fact that 3 was also a twin. The HKL files
used were in both cases limited to 408 in 2q. The Alerts pro-
duced by the checkcifs are in a large majority due to these
difficulties in refining the crystal structures.
p-Methoxystyrene oxide: This compound was epoxidized
under basic conditions using sodium hypochlorite and bro-
mide salt, according to a procedure described in the litera-
[43]
ture. p-methoxystyrene (360 mg, 2.7 mmol, 1 equiv.), KBr
(485 mg, 4.1 mmol, 1.5 equiv.), acetonitrile (13 mL) and
KH PO buffer (0.5M, pH 10.4, 13 mL) were mixed and
2
4
warmed to 408C. Aqueous NaOCl solution (5 mL of an
Acros commercial solution, 5% available chlorine, 0.6M
NaOCl determined by titration, 3 mmol, 1.1 equiv.) was
added and the resulting mixture was stirred at 408C for
2
0 min. After this time, the reaction was quenched with
General Procedure for the Synthesis of Epoxides with
mCPBA
Na SO ·H O (1 g) and the mixture was extracted twice with
2
3
2
EtOAc (225 mL). The combined organic layers were dried
Na SO ) and evaporated under vacuum to afford the de-
(
2
4
To a stirred solution of olefin (2.22 mmol, 1 equiv.) in
sired epoxide as a pale yellow oil; yield:306 mg (68%). The
product was used for GC reference without further purifica-
CH Cl (10 mL) maintained at 0–58C with an ice bath was
2
2
added dropwise
a
solution of mCPBA (2.66 mmol,
1
3
tion. H NMR (400 MHz, CDCl ): d=7.21 (d, J =8.6 Hz,
2
3
H,H
1
.2 equiv.) in CH Cl (10 mL). At the end of the addition,
3
2
2
H, ArH), 6.89 (d, J =8.7 Hz, 2H, ArH), 3.81 [m, 1H,
H,H
2
the reaction mixture was stirred at room temperature for
h. The mixture was washed with 10% aqueous Na CO
Ar-CH(O)], 3.81 (s, 3H, OCH ), 3.13 [dd, J =5.33 Hz,
3
H,H
4
3
3
2
2
3
JH,H =4.1 Hz, 1H, ArCH(O)CH ], 2.81 [dd, J =5.33 Hz,
JH,H =2.6 Hz, 1H, ArCH(O)CH ]; EI-MS: m/z (%)=121.07
2
H,H
(
5ꢅ15 mL) and then with brine (15 mL). The organic phases
2
were dried with Na SO and the solvent evaporated under
+
+
2
4
(
100) [MÀHÀCO] , 122.12 (10) [MÀCO] , 149.98 (20).
vacuum to afford the desired epoxide. Unless stated, iden-
Phenyl disulfide: This compound was synthesized accord-
1
tification of the desired epoxides was based on the H NMR
[28b] 1
ing to the procedure described in the literature.
H NMR
spectra and GC-MS analyses of the crude reaction mixture
when conversion was quantitative.
cis-Stilbene oxide: The title product was further purified
by column chromatography on silica gel using petrol ether
(
400 MHz, CDCl ): d=7.50 (m, 4H, H-2 and H-6), 7.29 (m,
3
4
H, H-3 and H-5), 7.23 ( m, 2H, H-4).
and ethyl acetate as eluent (20:1) and isolated; yield: 37%.
General Epoxidation Procedure
1
H NMR (400 MHz, CDCl ): d=7.22–7.13 (m, 10H, ArH),
3
4
.38 (s, 2H, Ar-CH); EI-MS: m/z (%)=167.12 (100)
Organic solvents used for catalysis were degassed by nitro-
gen bubbling during 30 min. Stock solutions were freshly
prepared before use. Oxidant stock solutions were prepared
to the indicated concentration by dilution of aqueous com-
mercial solutions with the indicated organic solvent, as fol-
lows: H O stock from aqueous H O 35% wt, 11.6M;
+
+
+
[
(
MÀHÀCO] , 195.12 (50) [MÀH] , 196.12 (25) [M] ; R
f
petrol ether/AcOEt 5:1)=0.45.
b-Acetoxy-5,6-epoxycholestanes:
[36b,38]
3
A ratio of 28:72 in
favour of the a-epoxide was determined by integration of
the C-3 and C-6 proton signals in the H NMR of the crude
1
2
2
2
2
residues [d=5.00–4.89 (C-3) and 2.90 (C-6) for a-epoxide
TBHP stock from aqueous TBHP 70% wt, 7.24M. Complex
2 and the substrate were dissolved in the corresponding co-
solvent in a test tube under stirring and then cooled on an
ice bath. The oxidant solution was added in two (at t=0 min
and t=60 min) or three portions (at t=0 min, t=30 min
and t=60 min). The reaction was followed by GC, by taking
aliquots (0.1 mL) at different times. The aliquot was placed
in a tube containing 0.1 mL of a solution of Na S O
and d=4.81–4.72
b-Acetoxy-5,6-b-epoxycholestane: H NMR (400 MHz,
CDCl ): d=4.72–4.81 (m, 1H, H-3), 3.08 (d, J =2.0 Hz,
ACHTUNGTRENNUNG( C-3) and 3.08 (C-6) for b-epoxide].
1
3
3
H,H
1
H, H-6), 2.03 (s, 3H, 3-OAc), 1.00 (s, 3H, H-19), 0.89 (d,
3
JH,H =6.6 Hz, 3H, H-21), 0.85 and 0.86 (2d, J =6.5 Hz,
H,H
2
ꢅ3H, H-26 and H-27), 0.61 (s, 3H, H ), 2.20–0.90 (m, 28
18
H).
2
2
3
Adv. Synth. Catal. 2012, 354, 428 – 440
ꢃ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
437

Frederic Bruyneel et al.
FULL PAPERS
(
0.22 mmol, 2.2M) in water and then extracted 3 times with
(0.05 mL, 0.769 mmol, 310 equiv. vs. catalyst); H O 2.91M
2
2
diethyl ether (3ꢅ1 mL). The organic layers were combined
and dried over Na SO and then diluted with ethyl acetate
stock solution (in MeCN/water) added in three portions
(0.22 mL, then 2ꢅ0.11 mL, total 3.7 equiv.). Reaction time:
90 min.
Test of acidic/basic additives: Complex 2 (0.15 mL of a
0.01644M stock in MeCN, 0.00247 mmol, 0.7 mol%); 0.6 mL
stock solution in MeCN, containing styrene (0.576M,
2
4
before injection in GC. The relative amount of epoxide
formed was determined by GC, by comparison to unreacted
substrate. When an internal standard was added (benzoni-
trile or eicosane), yields were determined by comparison
with the benzonitrile as internal standard (IS), using the
area ratio detected in GC and the calibration curves for
each pair of IS/substrate and IS/epoxide.
0.346 mmol,
0.173 mmol); acid or basic additive (0.05 mL of a 0.2M
aqueous stock, 0.01 mmol, 2.9 mol%); H 2.91M stock so-
1 equiv.)
and
benzonitrile
(0.288M,
O
2
2
Test of solvent influence: Complex 2 (3 mg, 0.0049 mmol,
.7 mol%); styrene (0.08 mL, 0.696 mmol, 1 equiv.); co-sol-
lution (in MeCN/water) added in three portions (0.22 mL,
then 2ꢅ0.11 mL, total 3.7 equiv.). Reaction time: 90 min.
0
vent (0.6 mL); H O 5.35M stock solution (in acetone/
Epoxidation of representative alkenes: Complex
0.15 mL of a 0.01644M stock in MeCN, 0.00247 mmol,
.7 mol%); 0.6 mL stock solution in MeCN, containing sub-
strate (0.576M, 0.346 mmol, 1 equiv.) and benzonitrile
0.288M, 0.173 mmol); thiophenol (0.045 mL of a 0.307M
stock in MeCN, 0.0138 mmol, 4 mol%); H O 2.91M stock
2
2
2
(
water) added in two equal portions (2ꢅ0.8 mL, 2ꢅ
.14 mmol, 2ꢅ3 equiv.). The final ratio catalyst/styrene/oxi-
dant was 1/140/850. The ratio co-solvent/acetone/H O was
0
2
2
(
3
.3/1.2/1 during the first 60 min and 1.7/1.2/1 after 60 min.
Reaction time: 90 min.
Test of oxidant influence: Complex 2 (3 mg, 0.0049 mmol,
2
2
solution (in MeCN/water) added in three portions (0.22 mL,
then 2ꢅ0.11 mL, total 3.7 equiv.). The final ratio H O /sub-
0
(
.7 mol%); styrene (0.08 mL, 0.696 mmol, 1 equiv.); MeCN
0.6 mL); oxidant stock solutions added in two equal por-
tions, for a total of: H O (3.19M stock in MeCN/water,
2
2
strate/additive/catalyst was 520/140/5.6/1. Reaction time:
9
0 min.
2
2
Epoxidation of 3b-acetoxy-5-cholestene: Complex
2
0
.8 mL, 2.54 mmol, 3.6 equiv.), TBHP (3.62M stock in
MeCN/water, 0.7 mL, 2.54 mmol, 3.6 equiv.), NaOCl (0.7M
commercial aqueous solution, 1.68 mL, 1.26 mmol,
(
0
0.015 mL of a 0.01644M stock in MeCN, 0.000247 mmol,
.7 mol%); 0.06 mL stock solution in AcOEt, containing
substrate (0.573M, 0.03438 mmol, 1 equiv.) and eicosane
0.055M, 0.0033 mmol); AcOEt (0.14 mL); MeCN (0.5 mL);
thiophenol (0.005 mL of a 0.307M stock solution in MeCN,
.0015 mmol, 4 mol%); H O 2.91M stock solution (in
1
(
0
.8 equiv.), PhIO(Ac) (412 mg, 1.28 mmol, 1.8 equiv.), PhIO
2
(
276 mg, 1.26 mmol, 1.8 equiv.). When PhIO was used,
.4 mL of additional MeCN were added and the oxidant was
mostly insoluble in the reaction mixture. Reaction time:
0
2
2
MeCN/water) added in three portions (0.05 mL, then 2ꢅ
9
0 min.
0
.05 mL, total 13 equiv.). The final ratio H O /substrate/cata-
2 2
Test of additive influence: Complex
2
(2 mg,
lyst was 1800/140/1. Reaction time: 4 h.
0
1
.00324 mmol, 0.7 mol%); styrene (0.053 mL, 0.461 mmol,
equiv.); additive (3.2 to 3.7 mol%); H O 3.19M stock so-
2
2
lution (in MeCN/water) added in three portions (0.27 mL,
then 2ꢅ0.14 mL, total 3.9 equiv.). When the additive was
pyridine or phenol: complex 2 (0.00247 mmol); styrene
GC Analyses of the Catalytic Processes
À1
GC method 1 (flow He 1.1 mLmin ): Initial temperature
(8C)/time (min)/slope (8C/min)/time (min)/final temperature
(
0.348 mmol); MeCN (0.6 mL); additive (3.6 mol%); H O
2 2
2.91M stock solution (in MeCN/water) added in three por-
(
8C)/time (min) 100/3/15/9/235/0.1. Retention times for sub-
tions (0.22 mL, then 2ꢅ0.11 mL, total 3.6 equiv.). Reaction
time: 90 min.
strates, oxidized products, additives and standard: benzoni-
trile t =3.95 min; styrene t =3.39 min; styrene oxide t =
r
r
r
Influence of thiophenol concentration: Complex
0.15 mL of 0.01644M stock solution in MeCN,
.00247 mmol, 0.7 mol%); styrene (0.04 mL, 0.348 mmol,
equiv.); MeCN (0.45 mL); thiophenol (1–40 mol%); H O
2
4
.85 min; 1-phenyl-1.2-ethanediol t =7.29 min; p-methoxys-
r
(
a
tyrene t =5.8 min; p-methoxystyrene oxide t =7.24 min;
r
r
0
1
2
indene t =4.71 min; indene oxide t =6.49 min; cyclohexene
r
r
2
2
t =2.57 min; cyclohexene oxide t =3.18 min; 2-cyclohex-
r
r
.91M stock solution (in MeCN/water) added in three por-
ene-1-one t =3.55 min; 7-oxabicyclo ACTHUNGTERNN[UNG 4.1.0]-heptan-2-one t =
r
r
tions (0.22 mL, then 2ꢅ0.11 mL, total 3.6 equiv.). Reaction
time: 90 min.
Test of oxidized sulfur additives: Complex 2 (0.15 mL of
4
4
.25 min; 1-octene tr =2.87 min; 1,2-epoxyoctane tr =
.29 min; bicyclo[2.2.1]hept-2-ene tr =2.68 min; exo-2.3-
AHCTUNGTRENNUNG
epoxy-norbornane tr =3.77 min; thiophenol tr =3.90 min;
a
0
0.01644M stock solution in MeCN, 0.00247 mmol,
.7 mol%); 0.6 mL stock solution in MeCN, containing sty-
phenyl disulfide t =7.13 min.
GC method 2: (flow He 1.2 mLmin ): Initial tempera-
r
À1
rene (0.576M, 0.346 mmol, 1 equiv.) and benzonitrile
0.288M, 0.173 mmol); sulfur additive (0.045 mL of a
.307M stock in MeCN or water, 0.0138 mmol, 4 mol%);
H O 2.91M stock solution (in MeCN/water) added in three
ture (8C)/time (min)/slope (8C/min)/time (min)/final temper-
ature (8C)/time (min) 150/18/10/5/200/0.5. Retention times
for substrates, oxidized products and additives: benzonitrile
2.31 min; cis-stilbene t =6.96 min; cis-stilbene oxide t =
(
0
2
2
r
r
portions (0.22 mL, then 2ꢅ0.11 mL, total 3.7 equiv.). The
final ratio H O /substrate/additive/catalyst was 520/140/5.6/1.
Reaction time: 90 min.
8.92 min; trans-stilbene t =13.13 min; trans-stilbene oxide
r
2
2
tr =13.50 min.
À1
GC method 3: (flow He 1.1 mLmin ): Initial tempera-
Test of excess acid: Complex 2 (0.15 mL of a 0.01644M
stock in MeCN, 0.00247 mmol, 0.7 mol%); 0.6 mL stock so-
lution in MeCN, containing styrene (0.576M, 0.346 mmol,
ture (8C)/time (min)/slope (8C/min)/time (min)/final temper-
ature (8C)/time (min) 220/2/5/16/300/6. Retention times: ei-
cosane t =4.44 min; 3b-acetoxy-5-cholestene t =18.17 min;
r
r
1
equiv.) and benzonitrile (0.288M, 0.173 mmol); AcOH
3b-acetoxy-5,6-b-epoxycholestane t =19.39 min; 3b-acetoxy-
r
(
0.05 mL, 0.873 mmol, 350 equiv. vs. catalyst) or MeSO H
5,6-a-epoxycholestane t =20.23 min.
3
r
438
asc.wiley-vch.de
ꢃ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2012, 354, 428 – 440

Catalytic Epoxidation of Alkenes by the Manganese Complex of a Reduced Porphyrinogen Macrocycle
À1
GC-MS method (flow He 1.1 mLmin ): Initial tempera-
ture (8C)/time (min)/slope (8C/min)/time (min)/final temper-
ature (8C)/time (min) 100/3/15/9/235/0.1.
3026–3035; d) M. C. White, A. G. Doyle, E. N. Jacob-
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Acknowledgements
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993, 93, 847–860.
This work was supported by the Swiss National Science
Foundation and the University of Neuchꢀtel. We thank Guil-
laume Journot for contributing to the paper by performing
the epoxidation of cholesteryl acetate with mCPBA and the
corresponding calibration in analytical GC.
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4
6
r
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53.80 gmol ; monoclinic, P2 /c; T=173(2) K; a=
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A
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G
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